Apparatus for enameling wire

ABSTRACT

Wire enameling apparatus includes seriatum a preliminary heater, an enameling means, means to recover and burn solvent vapor evaporating from the enameled wire, and an oven. Means guide the wire in a plurality of passes through the enameling and coating means. Means utilize the combustion products for heating within the system.

United States Patent 11 1 Goyffon 1 Jan. 16, 1973 s41 APPARATUS FOR ENAMELING WIRE References Cited [75] Inventor: Roland A. Goyffon, Macon, France UNITED STATES PATENTS [73] Assignee: Societe Mafit Manufacture de Fils 2,889,806 6/1959 ConantW "iii/119.6 e

lsoles Taurus e 3,265,033 8/1966 Touze et a1 ..118/61 1,829,290 10/1931 Merrill .219/388 Flledi "9 2,943,598 7/1960- Newton 118/405 x [21] AWL No; 46 791 1,870,990 8/1932 Evans ..118/405 X 2,215,996 9/1940 Benton ..117/232 Rehted Appfi'cafion Data 3,369,922 2/1968 Svrchek ..117 132 [63] (ljggi tinutatirzin-in-c laart of Ser. No. 60,256, Aug. 14, Primary ExaminerfMorris Kama a an one Att0rneyF1eit, Gipple & Jacobson [30] Foreign Application Priority Data 57] ABSTRACT Aug. 22, 1966 France ..667379l 1 Wire enamellng apparatus includes seriatum a prelimi- [52] U S Cl 118/61 118/65 118/405 nary heater, an enameling means, means to recover [51] h 11/00 and burn solvent vapor evaporating from the ne'n nan-:1:11112111131118818884 65 405: eeemelee we end ee Meeneeeiee the wire in a plurality of passes through the enameling and coating means. Means utilize the combustion products for heating within the system.

4 Claims, 7 Drawing Figures PATENTEUJAHS ma I I 3.710.756

sum 1 0r 3 vROL AND A .GOTF ON Pmmlznm 15 I973 3.710.756

' SHEET 3 [IF 3 ATTORNEY! APPARATUS FOR ENAMELING WIRE This application is a continuation in a part of my application Ser. No. 660,256 filed Aug. 14, 1967 and now abandoned.

The invention relates to an apparatus for the continuous coating, in particular the enameling of wires, especially electric wires. In such an apparatus the wire is passed in a continuous manner through an applicator device for the coating of enamel (varnish, etc.) and through an oven for the drying and the polymerization of the coated layer.

Prior processes and apparatus for this purpose evaporate the solvent from the enamel by heat flowing from the exterior towards the center of the coated wire.

As will be explained below, this feature results in slow is free from cracks and/or is more durable.

The apparatus according to the invention is characterized by the fact that the wires are hot when they first arrive at the'applicator device, and that the evaporation of the solvent takesplace, for a major part, on the path of the wires outside the oven, by the flow of heat from the wire towards the exterior.

terized by the fact that the applicator device comprises means for ensuring that the flow of heat during the drying stage is from the wire towards the exterior. The apparatus includes preferably, a closed casing containing the enamel bath and the various die'blocks fed by this bath, according to the features of my U.S. Pat. No. 3,412,709 granted Nov. 26, 1968.

The invention will be well understood with the aid of the following complementary description as well as'the accompanying drawings, which complementary description and drawings are, of course, given merely by way of example.

In these'drawings:

7 FIG. 1 illustrates in schematic perspective an enameling apparatus according to a known process;

FIG. 2 illustrates in section the conditions of heat flow in the wire inside the oven during the drying of the enamel in the known process of FIG. 1;

FIG. 3 shows, in a view similar to FIG. 1, an embodiment of an apparatus accordingto the present inven-- tion for performing the process according to the invention;

, FIG. 4 is a partial section through the oven of the embodiment shown in FIG. 3;

FIG. 5 shows, in a view similarto FIG. 2,. the conditions of heat flow -in the wire during the drying of the enamel in the process according to the invention, outside the oven;

FIG. 6 shows, in a view similarto FIG. 3, part of a modification of the apparatus shown in FIG. 3; and

FIG. 7 shows, schematically, other parts of the apparatus of FIG. 6.

The following description relates to the continuous enameling of copper wires. v

First of all, the prior process used most frequently at present will be described. i

I The apparatus according to the invention is charac In this process, the wire 1 (FIG. 1), is displaced along a continuous path forming several passes. This wire is passed successively through the die blocs 2, generally freely open, of an applicator 3, and successive passes are separated from each other by other passes, in one direction and then in the other, through an oven 4.

The wire enters at A and leaves at B, after passing around at least 2 rollers 5 and 6 (which can have grooves for the passage of the wires). The wire to be coated, when it arrives at the inlet in the applicator 3, is

cold, because it is necessary to prevent this applicator from becoming heated, which would cause evaporation of the solvent from the bath. Thus, the wire 1, at the intake A, after having undergone, if necessary, annealing at 7, passes into a cooling bath 8. Similarly, after a first pass in the oven, the temperature of the wire at the inlet of the second die block 2 is arranged to remain moderate by cooling the wire between the oven and the applicator. This necessitates in particular that the speed of displacement of the wire must remain rather low.

This limitation of speed is a first disadvantage.

Another disadvantage resides in the fact that the cooling of the wire is required in all the exterior portions of the oven, and the evaporation of the solvent from the layer of enamel, which is applied to the wire during each pass in the applicator, takes-place solely by the action of the heat going from the exterior towards the interior of the wire, as illustrated by the arrows of FIG. 2.

The calorific exchanges inside the enamel coating (represented by reference numeral 9, FIG. 2) thus take place from the periphery towards the center. Now, as the pass in the oven causes the evaporation of the solvent and the polymerization of the enamel at the same time, and since the peripheral layer tends to polymerize before the total evacuation of the solvent, the result is that:

on the one hand, this process gives rise, if the solventis not entirely evacuated, to a rapid ageing of the enamel, which thus loses, in time, its dielectric qualities;

and on the other hand, it gives rise to cracked enamel (micro-cracks), these cracks being caused by the solvent vapors which, in order to escape, burst an already polymerized layer.

To avoid this latter disadvantage, there was no other solution than to carry out the polymerization at a relatively low temperature, and thus'to reduce the speed of enameling, or to have, at the price of serious complications and considerable cumbersomeness, an oven comprising:

a low temperature zone for the evaporation,

a high temperature zone for the polymerization.

These means, valid for vertical ovens, such as that described in U.S. Pat. No. 3,265,033, aredifficult to apply to horizontal ovens (excessive length of the oven, excessive sag of the wire), and are relatively slow.

To avoid these disadvantages, according to the present invention, the wire is maintained hot outside the oven, that is, at a temperature hereinafter called drying temperature comprised between the temperature of the enamel when applied and the polymerization temperature of the enamel. The evaporation of the solvent can thus take place, for a major part, along a path outside the oven.

It is essential that the temperature of the wire be between the two limits just mentioned. In fact, if it were less than the lower limit, the exchange of heat during evaporation would take place from the exterior towards the interior as in the prior art processes. If, on

the other hand, it reaches orexceeds the temperature of the polymerization oven, there would no longer be two successive steps of evaporation of the solvent and polymerization of the enamel; consequently the quality of the enamel would be unfavorably affected.

Thus on the one hand, the role of the oven can be reduced to polymerization, the heat acting on the enamel from which the solvent is already evaporated, which leads to the absence of cracks, an on .the other hand, a higher speed can be used, since it is no longer necessary to cool the wire before its arrival at the die blocks 2.

It is then appropriate, preferably, to use a closed applicator, of the type described in the above identified patent application, the bath being contained in this applicator in a closed container which only communicates with the outside through the die blocks 2 or the holes leading to these die blocks.

For example, if the polymerization temperature of the oven 4 is of the order of 500C, the portions of the wire outside the oven can be maintained at temperatures of the order of 120 to 150C, whereas the applicator itself is, for example, at a temperature of the order of 50C and preferably under pressure. As for the speed of translation of the wire, which can reach values of the order of 700 meters/min, even 900 meters/min (in particular for 9/ 100 mm wire), instead of about 80 meters/min in the existing processes. Of course, these figures are given by way of example and are not to be regarded as limiting the scope of the invention.

In the table below are shown the production speeds obtainable with various enamels by the method according to the invention compared with the conventional method. The wire was 9/100 mm. diameter and the enamel was applied in a xylenol/cresol based solvent.

TABLE Conventional Method Method of invention Enamel Wire Quality of Wire Quality of speed Speed m/min Product m/min Product Polyurethane 200 Difficult to 850 Free of maintain micro-cracks; quality of Polyester I product at 500 enamel these wire flexible and Oil-base 70 speeds 400 durable means of two pullies 11 and 12 carried by pivoting rods 13 and 14.

cally all of the solvent already evaporated in the inter-,

val between the applicator and the oven. FIG. 5 shows the manner in which the thermal exchange takes place in the portions of the wire outside the oven: these portions are hotter than their surroundings, so that the thermal exchange takes place towards the exterior of the wire, assuring the free evaporation of the solvent.

The result is that, in the oven, the polymerization will be able to take place properly without risk of cracks, since the solvent has already evaporated. I

Needless to say, this evaporation can take place in free air, by using, for example, a fume hood, or any sort of tunnel comprising suction means, placed in front of the polymerization oven andcompletely independent of this oven. 5

In FIG. 6, there is shown a modification of the apparatus described above and illustrated by FIG. 3, this modification including a fume hood l-I provided with an evacuation chimney C.

In order not to reject the vapor captured by the fume hood directly into the atmosphere in the apparatus of FIG. 6, the arrangement shown in FIG. 7 can be used, which permits the recovery of the calories from the solvent vapor by subjecting this vapor to catalytic combustion.

This apparatus comprises, first of all, a suction device or fan 20 which, through the fume hood H, sucks the solvent vapor at the outlet of the applicator 3, and directs this vapor to a heat-exchanger 21 where it is re-heated, and then through a conduit 22 towards a combustion chamber 23 in which its temperature is first of all raised by heating means such as resistances 24, before the vapor passes to the catalytic combustion device 25. V i

The burnt gas is sucked by a fan 26 and a first part (the larger part) is directed through the conduit 27 towards the polymerization oven 4, whereas the other part is rejected through a conduit 28 to the free air, after having served for the re-heating of the solvent vapor in the exchanger 21. The part of the burnt gas which is directed towards the polymerization oven follows the path indicated by arrows inside thisoven (the oven operates, as can be seen, by radiation and by convection) and returns through a conduit 29 towards the combustion chamber 23, after mixing with the solvent vapor coming from the exchanger 21.

By modifying the operating conditions of the fans and by actuating regulating valves, in particular 30, 31 and 32 (placed respectively upstream of the fan 20 and downstream of the fan 26 in the conduits 27 and 28), all the possible adjustments of pressure (overpressure and underpressure) and discharge. can be obtained.

Itis clear from the foregoing that only burnt gas enters the polymerization oven or is rejected into the atmosphere, and this permits the recovery of the calories of this gas.

It can be seen that, in each of the above embodiments, the entire length of the oven remains available or the polymerization. Moreover, it is then possible to increase the temperature in the oven as much as the construction of the oven permits. The speed of enameling will then be adapted to this temperature so that, finally, the enamel will reach the ideal temperature of polymerization. The distance between the applicator of the oven will-be sufficient to permit the evaporation of the solvent before the wire penetrates into the heating tunnel. Experience has shown that this distance can be small.

It is appropriate to add that the process according to the invention permits the use of enamel having a high percentage of dry extract. The quantity of the solvent to be evaporated will thus be reduced, and accordingly, the distance between the applicator and the polymerization oven can also be reduced. For example, a percentage of dry extract of the order of 60 percent of the original total of enamel and solvent can be attained. It will also be apparent that the solvent may be a liquid vehicle in which the enamel or enamel-forming component is carried in suspension rather than in solution.

As a result, whatever. embodiment is adopted, a process and an apparatus are provided by which wires can be enameled in conditions which have numerous advantages with respect to previously known processes, in particular:

the possibility of high production speeds of the enamelled wire,

the possibility of eliminating the micro-cracks, and in any case, vof improving the quality of the finished product.

and the possibility of using an enamel having a high percentage of dry extract.

In a general manner, while the above description discloses what are deemed to be practical and efficient embodiments of the present invention, the invention is not limited thereto, and there might be changes made without departing from the inventive concept.

- Iclaim:

1. Apparatus for continuously enamelling wire comprising: wire feeding means arranged to move the wire axially of itself,

heating means,

an applicator positioned downstream of said heating means and comprising a closed container adapted to contain enamel including a solvent,

an oven spaced apart from said applicator,

said feeding means being adapted to feed said wire first through said heating means, and then successively through said applicator and said oven,

said heating means being adapted to heat the wire as it passes therethrough, to a drying temperature between the temperature of the enamel at the time of its application and the temperature of polymerization of the enamel, said applicator being arranged to apply a coating of said enamel to said wire at said drying temperature as said heated wire passes through said applicator, means for ensuring that the solvent in said coating is evaporated by flow of heat from the wire to the exterior, said oven being spaced sufficiently far from said applicator to allow at least a major portion of.

the solvent to evaporate from the coating before the wire passes into the oven, and said oven being further adapted to polymerize the enamel in the coating as the wire passes through the oven,

a fume-hood mounted between said applicator and said oven for'evacuating the solvent vapor as said solvent evaporates from the enamel coating,

a heat exchanger connected to said fume-hood and adapted to receive and to heat the solvent vapor coming from said fume-hood,

catalytic combustion means connected to said heat exchanger and adapted to receive and to burn said heated solvent vapor coming from said heat exchanger, thereby producing hot gas as a combustion product,

means for passing a part of said hot gas to said heat exchanger toheat the solvent vapor, and

means for passing another part of said hot gas to said oven to provide at least part of the heating in the oven.

2. Apparatus according to claim 1 in which said feeding means is adapted to feed the wire, after said wire has passed once throughsaid heating means, said applicator and said oven, cyclically through said applicator and said oven for a plurality of cycles.

3. Apparatus according to claim 2 in which said heating means forms a part of said oven.

4. Apparatus according to claim 1 in which said oven is adapted to receive the wire horizontally, and said feeding means are adapted to feed the wire horizontally. through-said oven. 

1. Apparatus for continuously enamelling wire comprising: wire feeding means arranged to move the wire axially of itself, heating means, an applicator positioned downstream of said heating means and comprising a closed container adapted to contain enamel including a solvent, an oven spaced apart from said applicator, said feeding means being adapted to feed said wire first through said heating means, and then successively through said applicator and said oven, said heating means being adapted to heat the wire as it passes therethrough, to a drying temperature between the temperature of the enamel at the time of its application and the temperature of polymerization of the enamel, said applicator being arranged to apply a coating of said enamel to said wire at said drying temperature as said heated wire passes through said applicator, means for ensuring that the solvent in said coating is evaporated by flow of heat from the wire to the exterior, said oven being spaced sufficiently far from said applicator to allow at least a major portion of the solvent to evaporate from the coating before the wire passes into the oven, and said oven being further adapted to polymerize the enamel in the coating as the wire passes through the oven, a fume-hood mounted between said applicator and said oven for evacuating the solvent vapor as said solvent evaporates from the enamel coating, a heat exchanger connected to said fume-hood and adapted to receive and to heat the solvent vapor coming from said fumehood, catalytic combustion means connected to said heat exchanger and adapted to receive and to burn said heated solvent vapor coming from said heat exchanger, thereby producing hot gas as a combustion product, means for passing a part of said hot gas to said heat exchanger to heat the solvent vapor, and means for passing another part of said hot gas to said oven to provide at least part of the heating in the oven.
 2. Apparatus according to claim 1 in which said feeding means is adapted to feed the wire, after said wire has passed once through said heating means, said applicator and said oven, cyclically through said applicator and said oven for a plurality of cycles.
 3. Apparatus according to claim 2 in which said heating means forms a part of said oven.
 4. Apparatus according to claim 1 in which said oven is adapted to receive the wire horizontally, and said feeding means are adapted to feed the wire horizontally through said oven. 